1. Field of the Invention
This invention relates to self-drilling and self-tapping screws, and to a method and apparatus for forming the self-drilling portion of the screw. Various methods and apparatus have been used in the past to form the cutting tip and flutes on the self-drilling portion of a screw blank which is to be formed into a self-drilling and self-tapping screw. These prior art methods and apparatus have been used to manufacture self-drilling and self-tapping screws which provide various characteristics in terms of torque required to drill and thread the screw into work pieces, and the relative easy and efficiency with which the screw is manufactured. The desired configuration of the cutting tip and of the flutes determined the method and apparatus required to shape a screw blank, and conversely the method and apparatus used determined to some extent the ability to provide the desired configuration of the cutting tip and flutes.
2. Description of Related Art Including Information Disclosed under Secs. 1.97-1.99
Reflecting the various manufacturing and screw performance objectives, numerous patents have issued in the past directed to methods and apparatus for forming self-drilling and self-tapping screws and the screws formed thereby. Some of these patents, and more particularly those wherein the point and flutes of self-tapping screws are formed by a sawing operation, are as follows:
______________________________________ U.S. PAT. NO. INVENTOR(S) ______________________________________ 3,231,132 Hanneman 3,280,412 Hanneman et al 3,288,015 Hanneman 3,422,472 Pomernacki 3,738,218 Gutshall 3,780,389 Lindstrom 4,071,918 Baer ______________________________________
All of the above-mentioned patents disclose various methods or apparatuses for manufacturing self-drilling and self-tapping screws, by which the points or flutes are formed by rotary cutters. The cutting teeth are located on the periphery of a cylindrical or disk shaped cutter. U.S. Pat. No. 3,231,132--Hanneman reveals an apparatus for forming drill pointed thread cutting screws wherein the point is formed by a milling cutter with a V-shaped cutting edge and the flutes are formed by offset saws fixed in position with respect to each other.
U.S. Pat. No. 3,280,412--Hanneman et al, reveals an apparatus wherein rotating milling cutters rotate into and out of engagement with the screw blank, but which do not move laterally with respect to the screw blank during the cutting operation so as to form an elongated slot.
U.S. Pat. No. 3,288,015--Hanneman, reveals a drilling and thread forming screw wherein the diameter of a rotary cutter determines the curvature of the slot surface.
U.S. Pat. No. 3,422,472--Pomernacki, reveals a method and apparatus for making drill screws wherein a pair of saws at different operation stations are used to form the pointed tip, and a second pair of saws also located at different stations are used to form the slots or flutes. The saws which form the slots or flutes do not move longitudinally with respect to the screw blank during the cutting operation so as to form an elongated flute.
U.S. Pat. No. 3,738,218--Gutshall, reveals a drilling and thread forming fastener wherein the groove or slot is formed by a cutter with a circular head having end cutting teeth.
U.S. Pat. No. 3,780,389--Lindstrom, reveals a method of manufacturing of self-drilling and self-tapping fasteners wherein grooves are formed by rotating cutters which do not move longitudinally with respect to the screw blank while cutting the groove.
Finally, U.S. Pat. No. 4,071,918--Baer, reveals a method of producing drill screws wherein a single rotary saw is located at each work station. Thus, the pointing operation is formed at two stations, and the fluting operation, which involves cutting by two saws to form each flute, is performed at four stations. Neither of the pairs of rotary saws used to form a flute moves longitudinally with respect to the blank as it is cutting the flute.